This invention relates to an optical module, which is an optical-electrical converting component between an optical fiber and an electronic circuit, for example, an optical module mounted in a transceiver and the like for a LAN system such as a G-bit ethernet, an optical element attachment method, and a receptacle-fitted optical module.
An optical module is an optical-electrical converting component wherein optical elements such as an LD (for example, using a face light-emitting-type semiconductor laser) and a PD (photodiode) are mounted on a lead frame, and these are sealed in a resin package (package for optical module). Usually, the optical module is connected to external optical wires by a single-filament or multi-filament optical connector section, attached to the package side face. For example, an SC-type ferrule corresponding to an SC connector is often used as the single-filament optical connector section which is attached to the package side face, and an MT(mechanically transferable)-type ferrule corresponding to a two-filament MT connector is often used as the multi-filament optical connector section.
The MT connector is an optical connector comprising optical fibers which are inserted and secured in a ferrule forming a joint face, and is thereby pin-fitted in position. Since the MT connector is stipulated by Japanese Industrial Standards JIS (plastic multi-filament optical fiber connector, JIS C5981), it will not be explained in detail.
FIG. 36 is a plan view of an example of a conventional optical module 1 when the cap is removed. Reference numeral 2 represents a package for optical module, 3 represents optical elements (3a showing the LD, and 3b showing the PD), 4 represents a mount which the optical elements 3 are mounted on, 5 represents an optical connector section comprising a ferrule, 6 represents optical fibers which are inserted into the ferrule 5 and secured therein, 7 represents lead terminals, and 8 represents an external optical connector which is attached to the tip of an optical fiber 9.
In the same way as a two-filament MT connector, the ferrule 5 shown in the diagram can be positioned by a pin-coupling method, thereby butt-connecting the optical fibers. Two optical fibers 6 are inserted and secured in the ferrule 5, and extend straight into the package 2 as a result of their own rigidity. When assembling the optical module 1 using this two-filament MT-type optical ferrule 5, the extending sections 6a of said two optical fibers 6 must be position-centered (axis-aligned) with the light-receiving face and light-emitting face of the optical elements 3 in order to achieve optimum effectiveness. Incidentally, since the optical fibers 6 cannot actually be moved, position-centering is carried out by adjusting the position of the optical element side.
There are two types of method for correctly aligning the tips of the optical fibers 6, which have been inserted and secured in the ferrule 5, with the optical element, as follows:    (1) Make the distance between the optical elements 3 and the side face which faces to the inside of the package 2 of the ferrule 5 as short as possible, and align and connect the tips of the optical fibers 6 to the optical elements 3. In this case, after positioning has been completed, the tips of the optical fibers 6 are affixed to the optical elements 3 by using an adhesive.    (2) Provide a positioning stand for positioning the optical fibers 6 in the correct positions between the ferrule 5 and the optical elements 3.
The positioning stand usually comprises two straight V-grooves, the extending sections 6a of the optical fibers 6 which extend from the ferrule 5 being secured on the positioning stand and positioned in a predetermined position and a predetermined direction.
The abovementioned positioning methods (1) and (2) have merits and demerits. In the case of (i), although the number of connection points is small, it is not possible to provide a sufficient gap between the ferrule 5 and the optical elements 3, and consequently there are problems that there is little freedom of design and adjustment is difficult.
For this reason, the method of (2), which provides a positioning stand fitted with V-grooves, is generally employed. The ferrule need not be fitted afterwards, but can be molded (the lower half of the ferrule) simultaneous to molding the package. In this case, there is an aspect in which, when the ferrule section is provided so as to extend to the inside, and the positioning stand fitted with V-grooves and the ferrule become a single unit, the positioning stand need not be molded as a separate body but can be directly connected.
There are two methods, termed active alignment and passive alignment, to carry out positioning between the optical fibers 6 and a semiconductor element. According to the active method, while emitting and receiving light by using an optical element, the optical power is monitored by using a gauge so that the optical power input/output efficiency with the optical fibers becomes an optimum value, and the position of the optical element is minutely adjusted. Marks and the like for positioning are provided on the optical element. These marks are monitored by a TV camera and the like while minutely adjusting the position of the optical element so as to match the marks showing the appropriate position inside the package. The passive method is a method for structural positioning.
In the active method, the adjustment is made while measuring the optical power. Therefore, an expensive special-purpose position-adjusting apparatus is required, with consequent drawbacks that time and labor are consumed.
In the passive method, adjustment is easy but precision is circumspect.